Inferno: Florence to Istanbul

Langdon wakes in a Florence hospital with a head wound and no memory of the last few days. When an assassin, Vayentha, turns up at the hospital, his doctor Sienna Brooks helps him escape. Later the pair slip into the Palazzo Vecchio using the Vasari Corridor, the raised passage that Duke Cosimo I de' Medici commissioned from Giorgio Vasari in 1564. It still connects the Palazzo Vecchio with the Palazzo Pitti.

Inside the Palazzo Vecchio, Langdon and Brooks find the phrase they are hunting in Vasari's painting The Battle of Marciano, in the Hall of the Five Hundred. Museum guide Marta Alvarez recognises Langdon: the night before, she showed him and Ignazio Busoni, director of Il Duomo, Dante's death mask. Now the mask is gone. The hall is vast, about 52 metres long and 18 metres high, and Vasari's monumental stairs lead up to it.

Visitor guidance: The Palazzo Vecchio is a museum on Piazza della Signoria; the Salone dei Cinquecento is on the second floor.

Langdon connects the phrase "Paradise 25" to the Florence Baptistry. There they find the Dante death mask holding a hidden riddle from its owner, the billionaire geneticist Bertrand Zobrist. The real Baptistery is octagonal in plan and dedicated to John the Baptist, the patron saint of Florence. The riddle sends the hunt on to Venice.

Visitor guidance: Check current opening times before visiting.

The riddle leads to Venice and St Mark's Basilica, where Langdon draws text from Doré's illustration Dandolo Preaching the Crusade at St. Mark's Basilica. The church is attached to the Doge's Palace on St Mark's Square. Look up at its four gilded bronze horses: they were among the early spoils brought from Constantinople after the Fourth Crusade.

Visitor guidance: The basilica stands on Piazza San Marco, next to the Doge's Palace.

In Istanbul the team conclude that Zobrist's clues point to the Hagia Sophia. The great building was raised by the Byzantine emperor Justinian I between 532 and 537. In the novel it is the landmark that leads the searchers to the hidden plague, which turns out to be in the cistern close by.

Visitor guidance: In Sultanahmet; check current visiting rules and times before going.

The plague is in the Cistern, but Brooks is already there. Fifty-two stone steps lead down into the vast underground hall, held up by a forest of 336 marble columns and built in the 6th century in the reign of the Byzantine emperor Justinian. Look for the inverted Medusa pillar, which features in the novel. It is the end of the trail that began in a Florence hospital bed.

Visitor guidance: Check current opening times before visiting.